Short note: extracellular export and consumption of glucose in Antarctic sea ice

Extracellular carbohydrate production is widespread in sea ice microbial communities, being produced by both algae and bacteria. Under stressful conditions, including nutrient limitation and high light, cells may export excess fixed carbon as glucose. Glucose microsensors were used to measure extracellular glucose exudation and consumption in a sea ice algal community. Glucose export increased with increasing irradiance between 15 and 512 µmol photons m⁻² s⁻¹. This export correlated with declining F_vF_m values and increasing NPQ values, implying that glucose export resulted from exposure to above optimal irradiances. Glucose concentrations in samples treated with DCMU to block photosynthesis, declined at all irradiances. Bacterial consumption of glucose was between 6 and 34% of extracellular export per hour. There have been very few measurements of DOC/glucose in sea ice and the data presented here make an important contribution to our understanding of sea ice microbial processes.